/**
 * Copyright 2012-2020 The Feign Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */
package feign.jackson;

import static feign.Util.UTF_8;
import static feign.Util.ensureClosed;

import java.io.BufferedReader;
import java.io.Closeable;
import java.io.IOException;
import java.io.Reader;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Collections;
import java.util.Iterator;
import java.util.NoSuchElementException;

import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.Module;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ObjectReader;
import com.fasterxml.jackson.databind.RuntimeJsonMappingException;

import feign.Response;
import feign.codec.DecodeException;
import feign.codec.Decoder;

/**
 * Jackson decoder which return a closeable iterator. Returned iterator
 * auto-close the {@code Response} when it reached json array end or failed to
 * parse stream. If this iterator is not fetched till the end, it has to be
 * casted to {@code Closeable} and explicity {@code Closeable#close} by the
 * consumer.
 * <p>
 * <p>
 * <p>
 * Example: <br>
 *
 * <pre>
 * <code>
 * Feign.builder()
 *   .decoder(JacksonIteratorDecoder.create())
 *   .doNotCloseAfterDecode() // Required to fetch the iterator after the response is processed, need to be close
 *   .target(GitHub.class, "https://api.github.com");
 * interface GitHub {
 *  {@literal @}RequestLine("GET /repos/{owner}/{repo}/contributors")
 *   Iterator<Contributor> contributors(@Param("owner") String owner, @Param("repo") String repo);
 * }</code>
 * </pre>
 */
public final class JacksonIteratorDecoder implements Decoder {

	private final ObjectMapper mapper;

	JacksonIteratorDecoder(ObjectMapper mapper) {
		this.mapper = mapper;
	}

	@Override
	public Object decode(Response response, Type type) throws IOException {
		if (response.body() == null)
			return null;
		Reader reader = response.body().asReader(UTF_8);
		if (!reader.markSupported()) {
			reader = new BufferedReader(reader, 1);
		}
		try {
			// Read the first byte to see if we have any data
			reader.mark(1);
			if (reader.read() == -1) {
				return null; // Eagerly returning null avoids "No content to map due to end-of-input"
			}
			reader.reset();
			return new JacksonIterator<Object>(actualIteratorTypeArgument(type), mapper, response, reader);
		} catch (RuntimeJsonMappingException e) {
			if (e.getCause() != null && e.getCause() instanceof IOException) {
				throw IOException.class.cast(e.getCause());
			}
			throw e;
		}
	}

	private static Type actualIteratorTypeArgument(Type type) {
		if (!(type instanceof ParameterizedType)) {
			throw new IllegalArgumentException("Not supported type " + type.toString());
		}
		ParameterizedType parameterizedType = (ParameterizedType) type;
		if (!Iterator.class.equals(parameterizedType.getRawType())) {
			throw new IllegalArgumentException("Not an iterator type " + parameterizedType.getRawType().toString());
		}
		return ((ParameterizedType) type).getActualTypeArguments()[0];
	}

	public static JacksonIteratorDecoder create() {
		return create(Collections.<Module>emptyList());
	}

	public static JacksonIteratorDecoder create(Iterable<Module> modules) {
		return new JacksonIteratorDecoder(new ObjectMapper()
				.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false).registerModules(modules));
	}

	public static JacksonIteratorDecoder create(ObjectMapper objectMapper) {
		return new JacksonIteratorDecoder(objectMapper);
	}

	static final class JacksonIterator<T> implements Iterator<T>, Closeable {
		private final Response response;
		private final JsonParser parser;
		private final ObjectReader objectReader;

		private T current;

		JacksonIterator(Type type, ObjectMapper mapper, Response response, Reader reader) throws IOException {
			this.response = response;
			this.parser = mapper.getFactory().createParser(reader);
			this.objectReader = mapper.reader().forType(mapper.constructType(type));
		}

		@Override
		public boolean hasNext() {
			if (current == null) {
				current = readNext();
			}
			return current != null;
		}

		private T readNext() {
			try {
				JsonToken jsonToken = parser.nextToken();
				if (jsonToken == null) {
					return null;
				}

				if (jsonToken == JsonToken.START_ARRAY) {
					jsonToken = parser.nextToken();
				}

				if (jsonToken == JsonToken.END_ARRAY) {
					ensureClosed(this);
					return null;
				}

				return objectReader.readValue(parser);
			} catch (IOException e) {
				// Input Stream closed automatically by parser
				throw new DecodeException(response.status(), e.getMessage(), response.request(), e);
			}
		}

		@Override
		public T next() {
			if (current != null) {
				T tmp = current;
				current = null;
				return tmp;
			}
			T next = readNext();
			if (next == null) {
				throw new NoSuchElementException();
			}
			return next;
		}

		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}

		@Override
		public void close() throws IOException {
			ensureClosed(this.response);
		}
	}
}
